Porsche Cayenne Hybrid (2007): first official pictures

Published: 26 July 2007

A Porsche hybrid?

That's right, and CAR Online has just returned from a visit to Weissach - Porsche's R&D HQ near Stuttgart - where we were given the full lowdown on the Cayenne Hybrid. Porsche's hand has been forced by the current public and political climate surrounding CO2 and global warming - and the company has taken the unusual step of showing its prototypes even though they're a few years from production. Porsche, like most other manufacturers, has been reducing its emissions in recent years, but it knows it must be publicly seen to be doing something green. Economy improvements must be shouted about, especially when the next car you will launch, in 12 months' time, will be a very large four-seat super saloon – the Panamera. The Cayenne Hybrid is the antidote to Porsche's wilder excesses, and it's being developed in conjunction with VW and Audi.

Surely there is another way?

Apparently not, at least not in the short term. It is too late in the Mk1 Cayenne’s lifecycle to start making drastic weight reductions. Lightweight body panels would reduce crash strength and, more importantly, are deemed too costly. Any thoughts of making the Cayenne a more road-focused vehicle are also a non-starter because the marketing people insist the car must at least match the Range Rover on the rough stuff. And apparently having the full breadth of 4x4 abilities is a must in important markets like the Middle East and China. Why doesn't Porsche build a diesel Cayenne? Porsche reckons derv engines are too heavy, thus reducing performance and steering feel. The company believes that however you crack crude oil, petrol will always be produced, so while it is available and deemed to be superior to diesel Porsche will use it. And so we have a Cayenne Hybrid that should lower CO2 emissions and fuel consumption, but still allow the company to use combustion engines.

So give me the details of the Cayenne Hybrid. Is it like a Lexus RX400h?

In a word, no. Porsche has gone for a ‘parallel hybrid’ system, which is modular so that the hybrid components can slot into the existing Cayenne architecture without the need for too many expensive changes. It sounds simple, but it is actually very complex. An RX400h has two electric motors, one for each axle, a battery, and a planetary set of gears. The Cayenne Hybrid has just one electric motor squeezed next to the V6 and still driving all four wheels. A Sanyo battery takes the place of the spare wheel; it's made of nickelmetalhydride (NiMH), and is fairly compact at 347 x 633 x 291mm so the boot floor is only raised by three inches. A can of tyre sealant replaces the spare wheel, or you can opt to have the wheel mounted on the tailgate. A clutch is fitted between the engine and regular transmission. When the clutch is open the engine turns itself off, be it in traffic or at speeds of up to 120kmh (75mph). This is where the Porsche differs from all other hybrids, because so long as there is sufficient charge in the battery, the Cayenne can run at motorway speeds on electric power. Porsche engineers call it ‘sailing along’.

But doesn’t shutting off the engine mean you lose all steering and brake assistance?

It would normally, but Porsche has developed a fully electric system for the brakes, steering and air-conditioning. The Cayenne's electrohydraulic steering alone accounts for 2.5 percent of the total fuel saving. Having a continuously functioning air-con system is crucial, not just for passenger comfort, but because the battery draws its cooling air from the interior compartment. The intake is mounted behind the left rear passenger and Porsche is currently working hard to reduce the noise from the system, which it deems is currently unacceptable.

Enough of the details, what’ll she do?

Engineers reckon the hybrid will cut half a second from the regular Cayenne’s 8.1 seconds on the benchmark 0-62mph. In-gear flexibility should also be improved as the electric motor kicks in to help. However, when your foot isn’t flat to the floor, the engine charges the battery as well as driving the car, so the V6 can also work at optimum loads for better fuel consumption. Porsche’s overall aim is to lower fuel consumption from 21.9mpg for the regular V6 to 31.8mpg on the hybrid. Currently, Porsche is at 28.8mpg but they're confident they'll hit their target with lower-rolling resistance tyres and other tweaks. What of CO2? A goal of 240g/km is mooted, well below the current V6’s 310g/km. Not bad when you consider that the hybrid system adds around 150kg to the V6’s kerb weight - including 69kg for the battery and a further 7kg for the crash protection around it.

It's a Porsche! Surely it's not just green, it must be fast as well?

You're right. This hybrid system will be nice to the environment, but it will also help you speed through it that bit quicker as well. The electric motor produces 34kW (45bhp) from standstill, with 210lb ft of twist available from 0-1050rpm. Combined with the V6, the hybrid has more than 369lb ft of twist on tap between 800-3200rpm. There's a stop/start function and regenerative braking, too. Press the brake pedal and the regular brakes apply, but then the regenerative brakes gradually take on more and more of the deceleration. This means the 38kW battery is charged under braking. Net benefit? It saves one litre of fuel for every 62 miles travelled. Porsche’s engineers are working on both stop/start and regenerative braking systems for the 911, Boxster and Cayman. However, that will take time, and in the medium term none of them will get the Cayenne’s Hybrid system, not least because it is only compatible with an automatic transmission.

Can the Cayenne Hybrid deliver its promises in the real world?

CAR Online got behind the wheel of a Cayenne Hybrid on a rolling road, and on a typical driving simulation achieved 26.1mpg. Usefully better than in a regular V6, but not exactly amazing economy - especially as we were pootling along at an average of just 27.1mph with only light throttle and braking. Of course, such lab conditions will always be somewhat artificial, though; what counts is the result on the open road. Ten minutes lapping the skid pan did however reveal the ‘sailing along’ system to be promising. With the battery at around half charge, the hybrid managed 700m at an indicated 28mph under full electric power. Not quite the 75mph electric-only cruise promised, but the production system should be capable of short bursts of motorway pace on electric power, or a longer cruise around town at 20mph - all with zero emissions. The switch between petrol and electric power was fairly imperceptible. The switch between friction and regenerative braking was equally unnoticeable, but then again it was a Porsche engineer at the wheel, so CAR Online will reserve full judgment until we've had our own feet on the pedals and hands on the wheel.

When does the Cayenne hybrid go on sale?

Before 2010, but that’s as far as Porsche will commit. That also means the Cayenne will be fairly long in the tooth when it finally gets the hybrid system. Also in the pipeline are Li-ion (lithium ion) batteries. The Weissach engineers are working with an unnamed supplier on this technology which holds a lot of potential. The current NiMH (above) battery’s weight and sized are predicted to be halved, whilst power will climb from 38kW at 288V to 55kW at over 400V. Such new battery technology could also allow a greater operating range and more efficient power usage. Such technology will not however appear before the Mk2 Cayenne, but it should account for a further reduction in fuel consumption by three percent.

Can the Cayenne Hybrid deliver its promises in the real world?

CAR Online got behind the wheel of a Cayenne Hybrid on a rolling road, and on a typical driving simulation achieved 26.1mpg. Usefully better than in a regular V6, but not exactly amazing economy - especially as we were pootling along at an average of just 27.1mph with only light throttle and braking. Of course, such lab conditions will always be somewhat artificial, though; what counts is the result on the open road. Ten minutes lapping the skid pan did however reveal the ‘sailing along’ system to be promising. With the battery at around half charge, the hybrid managed 700m at an indicated 28mph under full electric power. Not quite the 75mph electric-only cruise promised, but the production system should be capable of short bursts of motorway pace on electric power, or a longer cruise around town at 20mph - all with zero emissions. The switch between petrol and electric power was fairly imperceptible. The switch between friction and regenerative braking was equally unnoticeable, but then again it was a Porsche engineer at the wheel, so CAR Online will reserve full judgment until we've had our own feet on the pedals and hands on the wheel.

When does the Cayenne hybrid go on sale?

Before 2010, but that’s as far as Porsche will commit. That also means the Cayenne will be fairly long in the tooth when it finally gets the hybrid system. Also in the pipeline are Li-ion (lithium ion) batteries. The Weissach engineers are working with an unnamed supplier on this technology which holds a lot of potential. The current NiMH (above) battery’s weight and sized are predicted to be halved, whilst power will climb from 38kW at 288V to 55kW at over 400V. Such new battery technology could also allow a greater operating range and more efficient power usage. Such technology will not however appear before the Mk2 Cayenne, but it should account for a further reduction in fuel consumption by three percent.

By Ben Pulman

CAR's editor-at-large, co-ordinator, tallboy

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